A ball-throwing machine serves to help a player in exercising a ball sport. A kind of conventional ball-throwing machine employs resilient force, for example, provided by leaf springs, to bound out a ball. Another kind of conventional ball-throwing machine includes two throwing wheels rotatable in reverse directions. Via the rotational energy of the throwing wheels, the ball is thrown out of the ball-throwing machine. The throwing wheels can be tilted to change the angle of the thrown ball.
US Publication No. 2006/0137672 discloses an oscillating ball throwing machine, which includes a yoke assembly having two ball-throwing wheels. A first linkage is connected with the yoke assembly and drivable by a first motor. A second linkage and a cam are connected with the yoke assembly and drivable by a second motor. The first linkage can be driven by the first motor to move the yoke assembly to a nominal ball-throwing angle. The second linkage and the cam can be driven by the second motor to periodically oscillate the yoke assembly within an angle range two-degree plus and minus the nominal angle. Accordingly, the ball can be thrown out within a four-degree range so that the path and destination of the ball can be changed.
In Publication No. 2006/0137672, for controlling and changing the angle of the thrown ball, two motors, two linkages and one cam are needed to drive the yoke assembly.
Moreover, when setting function of a conventional ball-throwing machine, the ball-throwing operation still goes on. Under such circumstance, the ball is likely to hit a user and make the user injured.